Push down on the top/eraser end of your X-Tend mechanical pencil repeatedly to extend the pencil lead from the tip. If you extend it too far, press and hold down the top and then push the tip of the lead against the tabletop or your fingertip to slide the lead back into the barrel as much as desired.
Grasp the pencil between your fingers by the soft-grip near the tip and then write on surfaces as you would with any other writing tool. Push down on the eraser end whenever you need additional lead.
Press and hold down the top and then push the lead back into the barrel when you're finished using the pencil for the day.
Pull the eraser from the top and slide two replacement leads down the hole into the barrel when you run out of pencil lead. When finished, return the eraser to its holder -- pushing on it slightly to secure it in place. Push down on the top of the pencil two to three times to extend a lead.
Replace the eraser as soon as its top surface wears down to the top edge of its holder. Pry the remains of the old eraser out of the holder with the point of a safety or push pin and then push a new compatible eraser firmly into the holder to secure it.